I'm trying to exclude a row from a count if a specific column in this row is null.

More specifically to better describe the situation:

Service management, assigned and unassigned incidents. I'd like to count the tickets per priority that have been assigned to an employee.

count(${<[Incident.HuidigeActeur]<>null>}[_Flag_IncidentGesloten])

This is the formula I was trying to use (apologies for the Dutch field names)

To test whether or not it actually was excluding the null values I created the table below.

As you can see it is still counting the incidents that do not have an employee assigned to it. This makes me feel that my Set Analysis is incorrect, but if I'm doing something else incorrect please do inform me.